During one game last year, he doesn't remember which, Zach Zwinak trucked a safety so completely that he crushed the opposing player's facemask. An equipment manager for the team sent a photo to Penn State as proof.

"It was caved in when Zach ran him over," linebacker Glenn Carson said.

Zwinak, a 240-pound junior, begins 2013 as Penn State's No. 1 running back, a significant change over last August. Head coach Bill O'Brien placed Zwinak fourth on the depth chart last year, which he admitted was a mistake.

"That's some bad coaching," O'Brien said this week. Zwinak, though, climbed into the lineup on his own.

Taking advantage of injuries to other backs, Zwinak earned the starting spot and eventually rushed for 1,000 yards. He gained 589 of those in the last four Big Ten games, absorbing almost the entire backfield workload for the Lions.

A wrist injury in the Blue-White Game sent Zwinak to rehab this summer and limited his contact in training camp. Still, immediately after the injury, Zwinak told O'Brien that he would return for the first game.

"Because no matter what happened, I was going to work hard," Zwinak said this week. "I want to play, and I was going to play."

Zwinak spent the first two weeks of training camp wearing the red, no-contact jersey as a precaution. But that ended because defensive backs complained that Zwinak was hitting them while they weren't allowed to hit back. Zwinak said he found the red jersey "frustrating."

"I don't think I was playing to the rules of the red jersey," he said. "It was nice to have it off and be back to normal."

Running through contact is part of Zwinak's success. Last year he lost just 7 yards over 203 carries and made extra yardage on carries simply by falling forward. Which is how he was taught to run in high school.

"I love coaching Zach," O'Brien said. "He's very hard on himself. He demands perfection of himself. He's tough. He's a big guy. He can run. He's got deceptive speed, and you know, he
can catch the ball."

One issue O'Brien has pushed Zwinak to correct is ball security. The back lost four fumbles last year, including a critical drive-stopper in the loss to Nebraska.

Zwinak, who has gone through extra ball-security drills this year, admitted he's hard on himself about that issue.

"Numerous people tell me that I'm my toughest critic," he said. "... My dad taught me to do it the right way the first time. When that doesn't happen, I'm not very happy."